O'Donnell is the mother of Hoffman's three children, Cooper, 10, Tallulah, 7, and Willa, 5.
The will, written before Tallulah and Willa were born, includes specific requests as to where Cooper should live.
Hoffman said it was his "strong preference and desire but not direction" that Cooper should grow up in New York City, where the 46-year-old actor lived for many years, San Francisco or Chicago.
"If my guardian cannot reside in any of these cities, then it is my strong desire, and not direction, that my son, Cooper Hoffman, visit these cities at least twice per year throughout such guardianship," he added. "The purpose of this request is so that my son will be exposed to the culture, arts and architecture that such cities offer."
[CNN, ABC News]